青金石

• lapis lazuli is a rock composed primarily of lazurite, calcite, and pyrite (may also contain some hauynite, sodalite, with small amounts of diopside, augite, mica, and hornblende); chemical composition varies depending on mineral content 
• semitranslucent to opaque
• medium to dark, slightly greenish blue to violetish blue, often veined or flecked with brassy looking pyrite, and/or white to gray calcite inclusions
  

Identification

• Optic Character: AGG, if not opaque 
• Refractive Index: vague readings around 1.50, and sometimes 1.67, due to calcite
• Birefringence: none 
• Pleochroism: none 
• Ultraviolet Fluorescence: weak to moderate green or yellowish green (SW); calcite inclusions may fluoresce pink (LW) 
• Absorption Spectra: not diagnostic 
• Cause of Color: blue (in lazurite) – sulfur-related color centers 
• Specific Gravity: 2.75 (£.25), varies depending on mineral content 
• Polish Luster: waxy to vitreous 
• Fracture: granular, uneven
  Luster: dull 
• Cleavage: none
• Identifying Characteristics: commonly contains pyrite and white calcite, white to light blue distinctive fluorescence; rarely shows striated or “banded” structure
• Crystal Habit: massive
• Hardness: 5 to 6, varies with impurities 
• Toughness: fair 

Enhancements

• Method: dyeing

Effect: improves color, disguises calcite inclusions
Prevalence: common
Detectation: may be visible in cracks and pores; dye often comes off when rubbed with swab inned in acetone; also try denatured alcohol or dilute hydrochloric acid if no response to acetone
Stability: some dyes may fade or be washed out
Snecial Care Instructions: keep away from nail polish remover and other solvents
Method: paraffin coating or impregnation, oiling
Effect: to make the polish appear better; also to seal dye
Prevalence: common
Detection: hot point
Stability: fair
Special Care Instructions: avoid heat and solvents

Birthstone Designation(s)

• December birthstone
• 9th wedding anniversary

Major Sources: Afghanistan, Chile, USSR 

Stone information is reference from

Gem Reference Guide, Published by GIA. ISBN 0-87311-019-6

Gemstones of the World, Published by Sterling Publishing Co., Inc NY, ISBN 1-4027-4016-6

Encyclopedia of GEMSTONE, Published by ISHINSHA CO., LTD. ISBN 978-986-251-831-1